#ifndef GDT_H
#define GDT_H

#include <stdint.h>

#define SEG_DESCTYPE(x) ((x) << 0x04)
#define SEG_PRES(x)     ((x) << 0x07)
#define SEG_SAVL(x)     ((x) << 0x0C)
#define SEG_LONG(x)     ((x) << 0x0D)
#define SEG_SIZE(x)     ((x) << 0x0E)
#define SEG_GRAN(x)     ((x) << 0x0F)
#define SEG_PRIV(x)     (((x) & 0x03) << 0x05)

#define SEG_DATA_RD             0x00
#define SEG_DATA_RDA            0x01
#define SEG_DATA_RDWR           0x02
#define SEG_DATA_RDWRA          0x03
#define SEG_DATA_RDEXPD         0x04
#define SEG_DATA_RDEXPDA        0x05
#define SEG_DATA_RDWREXD        0x06
#define SEG_DATA_RDWREXDA       0x07
#define SEG_CODE_EX             0x08
#define SEG_CODE_EXA            0x09
#define SEG_CODE_EXRD           0x0A
#define SEG_CODE_EXRDA          0x0B
#define SEG_CODE_EXC            0x0C
#define SEG_CODE_EXCA           0x0D
#define SEG_CODE_EXRDC          0x0E
#define SEG_CODE_EXRDCA         0x0F

#define GDT_CODE_PL0    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
                        SEG_PRIV(0)     | SEG_CODE_EXRD

#define GDT_DATA_PL0    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
                        SEG_PRIV(0)     | SEG_CODE_RDWR

#define GDT_CODE_PL3    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
                        SEG_PRIV(3)     | SEG_DATA_EXRD

#define GDT_DATA_PL3    SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
                        SEG_LONG(0)     | SEG_SIZE(1) | SEG_GRAN(1) | \
                        SEG_PRIV(3)     | SEG_DATA_RDWR

struct gdt {
        uint16_t size;
        uint32_t offset;
} __attribute__((packed));

void flush_gdt(void);

uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag) {
        uint64_t descriptor;

        descriptor = limit              & 0x000F0000;
        descriptor |= (flag << 8)       & 0x00F0FF00;
        descriptor |= (base >> 16)      & 0x000000FF;
        descriptor |= base              & 0xFF000000;

        descriptor <<= 32;
        descriptor |= base << 16;
        descriptor |= limit & 0x0000FFFF;

        return descriptor;
}

#endif